1. Field of the Invention
This invention relates to an improved method of detecting flaws in a thread and, more particularly, to a thread inserter which will detect the knot in the reunited thread and subsequently insert the thread back into the fault sensing zone of the thread testing apparatus.
2. Description of the Prior Art
Devices are known in the prior art for detecting faults in a thread or yarn. Typically when the fault is detected, the yarn is then cut and the faulty area removed. The thread is then reunited with a knot and the spolling or knitting operation continues. One difficulty with prior art devices is that the fault sensing mechanism often has the inability to distinguish between short and long variations in thread size when the thread is motionless in the sensing zone. This can occur, for example, immediately following a thread uniting sequence when the thread is fed laterally into the sensing zone of the detecting device with little or no forward motion. Thus, a short thread imperfection which remains in the sensing zone for an extended period of time until the winding recommences is often treated by the sensing apparatus as identical to an elongated imperfection of the cross section in an advancing strand of thread. This may result in the thread being severed when, in fact, the true nature of the fault is such as to render that section of the thread as acceptable for winding.
One solution to the foregoing problem is discussed in detail in U.S. Pat. No. 3,389,867 entitled "Textile Apparatus" and issued on June 25, 1968 to Thomas E. Pitts. Since many of the features described in U.S. Pat. No. 3,389,867 are similar or identical to many of those which form a part of this invention, that patent is hereby incorporated in its entirety into this specification by reference. The Pitts' invention includes a delay mechanism which insures that the thread is moving before it reenters the sensing zone subsequent to its being reunited. If the delay is long enough, the knot itself may not enter the sensing zone or if it does enter the sensing zone is may be acceptable since the thread is moving.
Pitts provides two mechanisms for delaying the threads reentry into the sensing zone. One mechanism comprises a helical screw which rotates as the thread comes up to speed. Eventually the moving thread climbs to the top of the screw and naturally springs into the sensing zone. According to another embodiment an inclined cylinder is employed to delay the reentry of the thread into the sensing zone. One of the problems with such prior art devices is that they are difficult to correctly set in order to achieve thread reentry into the cutting zone at the appropriate point in the machine cycle. In addition, such delay devices frequently operate with "slippage" so that there are many unnecessary interruptions in the running of the machine and consequently many resettings are necessary. In addition to the foregoing the present invention is believed to be a simple and more efficient approach to the problem just described.